Radio frequency (RF) induction heating is ideally suited for material-processing technology and has been used for many years for melting, brazing, heat treating and crystal growth. In semiconductor processing, the main reason to prefer induction heating is cleanliness. Only the susceptor and wafer are subjected to high temperatures and the heating coil can be located outside the physical enclosure. Materials at very high temperature, which cannot be contained within a crucible, can be heated directly in an RF float-zone configuration or by levitation melting. The steel industry, for example, employs RF induction for annealing cylindrical billets prior to hot working because the process is the most efficient and the least contaminating.
Many frequencies have been used for induction heating from 60 Hertz line power up to several megahertz. In general, the lower frequencies are used with large size ferrous metal work and the higher frequencies with smaller loads of low and high resistivity, which are difficult to heat.